1. Field of the Invention
This invention relates to a spark gap device for use in an electrical filter connector.
2. Description of Related Art
In many electrical connector applications, it is essential that transient voltages be prevented from reaching electronic components within the electrical device to which the connector is connected. This is especially true in cases where the connector is used to connect a cable to the electrical device, and where there is a significant possibility that transients can arise within the cable, such as might occur in a local area network (LAN). As a result, numerous proposals have been implemented for placing filters within the connectors themselves, in order to prevent undesired voltages that arise outside of the electrical device from entering the device.
A common connector filtering scheme, first disclosed in U.S. Pat. No. 4,500,159, and also shown in U.S. Pat. No. 4,934,960, is to use relatively inexpensive miniature capacitor chips inserted into recesses in a dielectric connector body or housing, one electrode of the chips contacting an electrical signal contact in the connector, and the other being grounded via a metal clip fitted onto the connector body. However, the resulting miniature capacitive filters have a limited voltage handling capacity.
In a variation of the chip capacitor filtering scheme, the chip capacitors are connected between the outer contact of a BNC connector and panel to which the connector is attached, thereby decoupling the panel ground from the cable ground, except with respect to AC transients. As is the case with filtering capacitors, however, the decoupling chip capacitors are vulnerable to high voltage transients. Examples of this type of connector include the BNC connector shown in the Amphenol sales brochure entitled "Capacitively Decoupled BNC", Issue January 1991, and also the connector disclosed in U.S. Pat. No. 4,884,982.
Other examples of chip capacitor filtering or decoupling arrangements are also shown in U.S. Pat. No. 5,151,054 issued Sep. 29, 1992 and in U.S. Pat. Nos. 2,454,448, 3,324,335, 3,791,711, 4,293,887, 4,509,090, and 4,905,931.
One solution to the problem of low voltage handling capacity in chip capacitors is to use spark gap devices for shunting high voltage transients to ground, the conventional spark gap devices including a non-conductive gap in a conductive path capable of handling the abnormally large voltages that might, for example, be induced by a lightening strike. However, the cost of manufacturing conventional spark gap devices small enough to fit within the size requirements of a typical miniature connector is prohibitive, and the use of spark gaps in miniature filter or BNC connectors for the purpose of providing protection against larger voltages has therefore proved impractical.
Examples of discrete spark gap devices, or capacitor/spark gap combinations, are disclosed in U.S. Pat. Nos. 3,087,093, 3,271,619, 3,316,467, 3,484,842, 3,564,682, 3,668,458, 4,318,149, and 4,626,957. None of these devices is suitable for use in a capacitor chip type filter or BNC connector.
An example of a spark gap device which is described as being suitable for use in a BNC type connector is shown in the above-mentioned U.S. Pat. No. 4,884,982. However, use of this device requires modification of the conventional decoupled BNC housing and ground clip, and also the use of a separate dielectric in order to obtain the most accurate gap dimensions, all of which present problems in terms of both cost and efficiency.